I certainly love Pentagram. Also on the older side of things, I consider older Uriah Heep to be Metal. Listen to Rainbow Demon and Gypsy!

Black Sabbath, definitely. Candlemass on first two albums are superb. I also agree on Angel Witch and Judas Priest's Sad Wings Of Destiny. Iron Maiden's debut is flawless. I had always avoided having a "favorite song" until I heard Phantom Of The Opera. The perfect romanticist blend of early punk and progressive rock.

Motorhead are rock n' roll but it still never hurts to mention them in any discussion whatsoever!

Ah! Im glad you changed the sabbath entry from first 4 to first 6! Sabbotage is great.

I've never liked volume 4, oddly. They seem to go fully blues hard rock and loose what set them apart from other hard rock bands (apart from the first track, which is one of their best)

Apart from Master of Reality, and maybe Paranoid, a lot of their albums are really patchy. I feel the same way about most of the above bands. For whatever reason, artists in this genre aren't particularly consistent, even when they get it right. Maybe because of the proximity to rock/pop music?

Pentagram is a great band, at least on the stuff I'm familiar with. Their first full-length is midpaced-to-speedy doom/heavy metal in the style of quicker Sabbath songs like "Symptom of the Universe." They seem to have put a lot of thought into what riff goes with what, which makes sense since parts of the songs had been bandied about by the band since their early '70s days as a more Cream-like heavy blues rock band. The song structures do that cool Sabbath Bloody Sabbath thing where they start out like they're going to be verse/chorus, but then take a turn towards narrative songwriting in their second half. The lo-fi production is thick, dark, and crunchy, which greatly enhances the atmosphere.Their second album is even better, taking a turn towards both darker atmospheres and more progressive songwriting. They slow down the tempo to more of a crawl a lot of the time (probably because "doom metal" had become a more established series of tropes at this time with the rise of Saint Vitus and Candlemass), but they do a good job of keeping it from getting boring. There is a massive focus on intertwining dual guitar melodies this time around, as well as some more dynamic variation in the form of acoustic and undistorted guitar intros and segues. A lot of the songs feel quite layered and complex, with the aforementioned guitar melodies interacting with each other and the heavier riffs played "below" them in interesting ways. Perhaps a hidden precursor to stuff like diSEMBOWELMENT? If you, like me for years, have been avoiding Pentagram for whatever reason, I would highly recommend those two albums.

Saint Vitus has always been good, except perhaps on the C.O.D. album which many people point to as their sell-out album. I would suggest working through their discography chronologically from the S/T up through V, then pick up the the trail with Die Healing and the new full-length. The Dark Legions review does a good job of articulating what is cool about Saint Vitus.

The Soul Sacrifice EP and the second full-length are also worth listening to. They do a good job of picking up where Sabbath left off on their mid-'70s albums, when they started hanging out with the guys from Yes and moving towards more narrative songwriting and varied dynamics. After that, Cathedral gets a little bit too groovy fun-time for me.

Their second album is also great, and quite under-recognized nowadays. I feel like most of their songs were written all around the same time, with the slower ones going to the debut and the quicker ones going to the sophomore, but I could be wrong.

I'd also recommend Manilla Road from Invasion up through The Courts of Chaos, with their crowning achievements being Crystal Logic, The Deluge, and Open the Gates. They started out as kind of a heavy metal response to Hawkwind, got a bit more power metally and epic, and then went more towards a speed/thrash direction, before synthesizing all of those approaches on their 1990 album and then breaking up.

Their early classic "Cage of Mirrors" does a good job of summing up why they're a great band. They're willing to take chances, and more concerned with communicating interesting musical ideas than with writing radio hits or "being metal." This song starts off with what I'd call the "Cage" motif before crashing into a 2112 era Rush-style set of heavy riffs. It goes back and forth through that cycle a few times, with both the light "Cage" parts and the heavy sections introducing new variations with each cycle. The way that the motifs and variations link up with the lyrics both in mood and actual storyline content reminds me a lot of Wagner, who I'm sure was an influence. The vocals and production take some getting used to, but in the end, they end up fitting the music quite well.